We propose development of an on-line, continuous, modular, patient monitoring system controlled by a small digital computer. Capable of monitoring patients with only non-invasive sensor as well as those with intra-arterial, intra-venous, and intra-tracheal lines the system is designed both as a practical instrument and as a research tool for developing and testing new methods of monitoring. Four patients will be monitored simultaneously with options to follow heart rate, EKG arrhythmia diagnosis, respiratory rate, temperature, respiratory mechanics, arterial pressure, cardiac output, and indirect blood pressure. Display is on TV screen and paper output on a teletypewriter. Data storage will be on magnetic tape allowing 12 hours of graphic display and later off-line statistical analysis. The system is built around a relatively inexpensive digital computer (12-bit words size, 8K memory), and it will permit some exploration of other potential uses of mini-computers in clinical medicine.